Mass of a Meter Stick -- Torque Lab

Step 1 DEMO:

The meter stick was not balanced on the edge of the table and either fell, or was not actually in a balanced state, meaning that the torques of both sides of the stick were not equal. What is torque? It is the amount of force multiplied by the lever arm that ultimately creates a rotation of the system. The meter stick is the rotation in this lab.

After speculation, (the meter stick balanced at approximately 50cm) we took the meter stick and added a 100gram weight on the end. Once it was steady, the next goal was to balance the stick again, and measure the distance between the weight/(end off the table) and where the axis of rotation was. The lab asked for pictures labeling the center of gravity, the lever arm, and the force.

Step 2 PLAN: 

The equation we used to solve for the meter stick’s mass was derived from the idea that the torque on either side was equal when balanced. Because torque is force times distance, simply put, the new equation was (Fgravity)(distance) = (Fgravity)(distance). Fgravity, we learned in chapter 2, is the same term as weight, which equals (mass)(gravity).

Now: (mass)(gravity)(distance) = (mass)(gravity)(distance)

(0.1kg)(9.8)(30.5cm from table) = (x)(9.8)(19.5 from end of table to 50cm mark)

x = 0.156 kg  OR  156 grams

Percent error: (156 – 150.7) / 150.7 = 3.5% error!!

         

SUMMARY & Explanations – The method that worked…using Mr. Roo as a resource.

*Torque:  what makes an object or system rotate; (force)(lever arm)

*Lever arm:  the distance from the axis of rotation; more distance, easier to rotate

*Force:  a push or a pull on an object; Fgravity is just the weight

*Center of Mass:  where an object’s mass is in relation to the pull of gravity ¯

*Mass:  how much matter an object has

*Weight:  the force of gravity on an object’s mass

Why things are balanced: the torque is equal on either side of a rotating object/system. The bigger the lever arm, the less force is required to rotate the object. The smaller the lever arm, the more force is needed to rotate it. They’re inversely proportional.  

Here are some pictures I made from PowerPoint:

    

   CHEERS.